linux-kernel - Re: [PATCH] gpio: Add Tegra186 support

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Date:   Thu, 24 Nov 2016 16:08:41 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Laxman Dewangan <ldewangan@...dia.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Stephen Warren <swarren@...dotorg.org>,
        Suresh Mangipudi <smangipudi@...dia.com>,
        Alexandre Courbot <gnurou@...il.com>,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH] gpio: Add Tegra186 support

On Thu, Nov 24, 2016 at 08:14:31PM +0530, Laxman Dewangan wrote:
> 
> On Thursday 24 November 2016 08:14 PM, Thierry Reding wrote:
> > * PGP Signed by an unknown key
> > 
> > On Thu, Nov 24, 2016 at 12:23:56PM +0530, Laxman Dewangan wrote:
> > > On Tuesday 22 November 2016 11:25 PM, Thierry Reding wrote:
> > > > +static inline struct tegra_gpio *to_tegra_gpio(struct gpio_chip *chip)
> > > > +{
> > > > +	return container_of(chip, struct tegra_gpio, gpio);
> > > > +}
> > > You dont need this as gpiochip_get_data(chip); can provide the required
> > > driver specific data.
> > It's common practice to embed the struct gpio_chip within a driver-
> > specific structure, and it's equally common to use a container_of() to
> > get at the embedding structure.
> 
> I am saying that you dont need this new APIs, GPIO framework already support
> this via the call gpiochip_get_data(chip); which you provided when adding
> gpiochip().

Okay, it looks like this is the standard way to do this within the GPIO
subsystem. I can switch to that.

> > > > +	gpio->gpio.parent = &pdev->dev;
> > > > +
> > > > +	gpio->gpio.get_direction = tegra186_gpio_get_direction;
> > > > +	gpio->gpio.direction_input = tegra186_gpio_direction_input;
> > > > +	gpio->gpio.direction_output = tegra186_gpio_direction_output;
> > > > +	gpio->gpio.get = tegra186_gpio_get,
> > > > +	gpio->gpio.set = tegra186_gpio_set;
> > > > +	gpio->gpio.to_irq = tegra186_gpio_to_irq;
> > > > +
> > > > +	gpio->gpio.base = -1;
> > > > +
> > > > +	for (i = 0; i < gpio->soc->num_ports; i++)
> > > > +		gpio->gpio.ngpio += gpio->soc->ports[i].pins;
> > > > +
> > > Our DT binding does not say this. We assume that we have 8 gpios per port.
> > > so this will not work at all.
> > This has nothing to do with the device tree binding. What the device
> > tree binding defines is the indices to use to obtain a given GPIO within
> > a given port. What numbering the driver uses internally is completely up
> > to the driver implementation.
> > 
> > Oh, and the above works just fine.
> 
> 
> Nop, it will not work. The reason is:
> include/dt-binding/gpio/tegra186-gpio.h
> 
> 
> #define TEGRA_MAIN_GPIO(port, offset) \
>         ((TEGRA_MAIN_GPIO_PORT_##port * 8) + offset)
> 
> 
> so in your DTS file, if you use this macro for the gpio number then you will
> have pin per port as 8.
> And so your total GPIO is 23 *8 (Port CC) but in source code ngpio is very
> less.

Yes, within the source code, ngpio will be the exact number of pins that
the GPIO controller physically exposes. But that still works fine, feel
free to test the driver if you don't believe me. The translation from
one numberspace to the other is done in tegra186_gpio_of_xlate().

Thierry

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